EFFICIENT, LOCALITY-MAINTAINING NAMESPACE OPERATIONS IN A WRITE-OPTIMIZED FILE SYSTEM

There is a long-standing trade-off between good locality (fast directory traversals) and efficient namespace operations (efficient file or directory renames) in file systems. Traditional inode-based file systems have good rename performance but can fail to maintain locality, especially in the face of file system aging. On the other hand, full-path-indexed file systems ensure locality, however, renaming a directory needs to update all related full-paths, which is usually implemented as an expensive operation. No existing file system has both good locality and efficient namespace operations. This dissertation describes a new file system design that has both good locality and efficient namespace operations. In particular, we describe a novel synthesis of write-optimization, fullpath indexing, and operations on data structures. By directly manipulating the data structure, a full-path-indexed file system can efficiently update related full-paths in a rename. Moreover, with the technique, a full-path-indexed file system can clone a directory without traversing the directory. We implement this technique in BetrFS, a full-path-indexed, write-optimized, local file system for Linux. Compared to ext4, the widely used inode-based file system in Linux, the new version of BetrFS traverses the Linux source directory 9.47x faster and renames the same directory 1.09x faster. Meanwhile, the new version of BetrFS clones a directory faster than state-of-the-art file systems that support clones, such as Btrfs and XFS.Doctor of Philosoph